Method for quenching a gas stream in the production of vinyl chloride monomer

ABSTRACT

A method and apparatus for quenching a gas stream in the production of vinyl chloride monomer includes the use of a knock back condenser and a plurality of column fractional distillation trays disposed within the quench column, and a liquid stream of 1,2-dichloroethane, vinyl chloride, and hydrogen chloride may be removed from the bottom column fractional distillation tray.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and apparatus for quenching a gasstream in the production of vinyl chloride monomer and, moreparticularly, a method and quench column for quenching a gas streamcomprising vinyl chloride, hydrogen chloride, and unreacted1,2-dichloroethane.

2. Description of the Prior Art

Few monomers are commercially produced in the world on so large a scaleas vinyl chloride monomer ("VCM"). Over 95% of the VCM produced in theworld is made by pyrolysis of 1,2-dichloroethane, or ethylene dichloride("EDC"), in accordance with the following reaction: ##STR1## Thisreaction typically takes place at elevated temperatures in the range of900° F.-1000° F. within a cracking furnace having a plurality ofpyrolysis furnace tubes. The EDC is thermally cracked to produce equalmolar quantities of vinyl chloride and hydrogen chloride ("HCl").Typically the cracking furnace is designed to convert 50% to 60% of theEDC feed per pass of the feed through the cracking furnace. Hot crackingfurnace effluent gases containing vinyl chloride, hydrogen chloride,unreacted EDC, and undesired byproducts, including carbonaceousimpurities, such as coke, and chlorinated organics, must be rapidlycooled in a quench column to stop the pyrolysis reactions and tominimize the formation of additional byproducts. Typically, in the priorart, these effluent gases are cooled by direct contact with cooledliquid EDC and vinyl chloride in the quench column.

A major portion of a VCM manufacturing plant's capital and operatingcosts are associated with the separation and purification of thecracking furnace effluent gas components. Fractional distillationprocesses are typically used to separate VCM and HCl products, and areused to remove undesired impurities from unreacted EDC for recycling tothe cracking furnace feed stock.

There are many disadvantages associated with current quench columndesigns and methods of quenching utilized in the production of VCM. Onedisadvantage is the necessity to use relatively large capacitycirculation pumps and piping, which result in substantial capital costsin constructing a VCM plant. There are process safety and environmentalconcerns resulting from circulated liquid containing undesiredimpurities, such as coke particles, which can cause severe pumpmaintenance problems and piping erosion. Historically, cracking furnacequench circulation piping failures have been a major source for VCMproduction plant fires. Another disadvantage associated with prior artquench column designs and methods of quenching is that it is difficultto remove coke particles, which causes relatively high fouling rates onVCM purification equipment and reduces equipment life. A furtherdisadvantage associated with prior art quench column designs and methodsof quenching is that poor component separation is achieved, whichresults in higher energy costs for the conventional downstream hydrogenchloride and vinyl chloride distillation process. An additionaldisadvantage of conventional methods and apparatus for quenching thecracking furnace effluent gas stream is that removal of solids from thequench column, such as coke particles, is typically done by filteringquench liquid which is removed from the bottom of the quench column.Filtering efficiency is typically very poor because conventional methodsand apparatus tend to break up fragile coke particles into smallerparticles which can pass through the filtering device.

Accordingly, prior to development of the present invention, there hasbeen no method and apparatus for quenching a gas stream from an EDCcracking furnace which: does not require relatively large capacitycirculation pumps and piping and their substantial capital-costs; doesnot have process safety and environmental concerns arising fromcirculated liquid containing coke particles which can cause severe pumpmaintenance problems and piping erosion, and could lead to pipingfailures and resulting plant fires; easily permits the removal of cokeparticles from the quench column, whereby vinyl chloride purificationequipment does not have relatively high fouling rates, which reducesequipment life; achieves good component separation, which results inlower energy usage for the downstream hydrogen chloride and vinylchloride distillation process; and has substantial filtering efficiencyto remove fragile coke particles. Therefore, the art has sought a methodand apparatus for quenching a cracking furnace effluent gas streamwhich: does not require the use of relatively large capacity circulationpumps and piping, thereby having lower capital costs; does not haveprocess safety and environmental concerns resulting from circulatedliquid containing coke particles, thereby reducing pump maintenanceproblems and piping erosion; permits the easy removal of coke particlesto avoid high fouling rates on vinyl chloride purification equipment,and increases equipment life; provides good component separation, whichresults in lower energy usage for the downstream hydrogen chloride andvinyl chloride distillation process; and achieves high filteringefficiency for the removal of coke particles.

SUMMARY OF THE INVENTION

In accordance with the invention, the foregoing advantages have beenachieved through the present method of quenching a gas stream comprisingvinyl chloride, hydrogen chloride, and unreacted 1,2-dichloroethaneproduced by the pyrolysis of 1,2-dichloroethane and containing undesiredbyproducts of pyrolysis. The present invention may include the steps of:providing a quench column, having an upper and lower end, the lower endof the quench column containing a quantity of quench liquid; introducingthe gas stream directly into the quench liquid to cool the gas stream tocease the pyrolysis of the EDC and minimize the formation of additionalbyproducts, whereby EDC, vinyl chloride, and HCl vapors rise from thequench liquid; providing a plurality of column fractional distillationtrays, with at least an upper column fractional distillation tray and abottom fractional distillation tray, within the quench column above thequantity of quench liquid; passing the EDC, vinyl chloride, and HClvapors upwardly through the plurality of column fractional distillationtrays; introducing liquid EDC, vinyl chloride, and HCl into the upperend of the quench column, above the plurality of column fractionaldistillation trays; removing the EDC, vinyl chloride, and HCl vaporsfrom the upper end of the quench column; and removing a liquid stream ofEDC, vinyl chloride and HCl from the bottom column fractionaldistillation tray.

Another feature of the present invention is that the liquid EDC, vinylchloride, and HCl may be introduced into the upper end of the quenchcolumn by providing a knock back condenser in the upper end of thequench column above the column fractional distillation trays, andpartially condensing the rising EDC, vinyl chloride, and HCl vapors. Anadditional feature of the present invention is that the liquid EDC,vinyl chloride, and HCl may be introduced into the upper end of thequench column by providing a horizontally disposed condenser above thequench column; partially condensing the rising EDC, vinyl chloride, andHCl vapors; and introducing the liquid EDC, vinyl chloride, and HCl fromthe horizontally disposed condenser into the upper end of the quenchcolumn. The liquid EDC, vinyl chloride; and HCl may be flowed into theupper end of the quench column by only utilizing the force of gravity,whereby no pump is utilized to introduce the liquid EDC, vinyl chloride,and HCl. A further feature of the present invention may include the stepof removing from the bottom of the quench column a portion of the quenchliquid containing the undesired byproducts of pyrolysis, and filteringout the undesired byproducts of pyrolysis.

In accordance with another aspect of the present invention, theforegoing advantages have been achieved by the present quench column forquenching a gas stream comprising vinyl chloride, HCl, and unreacted EDCproduced by the pyrolysis of EDC and containing undesired byproducts ofpyrolysis. This aspect of the present invention may include: avertically disposed vessel having an upper and a lower end, the lowerend adapted to contain a quantity of quench liquid; at least one nozzledisposed in the lower end of the vessel and adapted to be disposedwithin the quantity of quench liquid; a plurality of column fractionaldistillation trays, with at least an upper column fractionaldistillation tray and a bottom column fractional distillation tray,disposed within the vessel, above the at least one nozzle; and a meansfor introducing liquid EDC, vinyl chloride, and HCl into the upper endof the vessel above the plurality of column fractional distillationtrays.

Another feature of this aspect of the present invention is that themeans for introducing may be a knock back condenser disposed in theupper end of the vessel above the column fractional distillation trays.A further feature of this aspect of the present invention is that themeans for introducing may be a horizontally disposed condenser disposedabove the vessel, and the liquid EDC, vinyl chloride and HCl flow fromthe horizontally disposed condenser into the upper end of the vesselonly under the force of gravity. An outlet means may be disposed at thelower end of the vessel for draining a portion of the quench liquid fromthe vessel, and the outlet means may be in fluid communication with ameans for filtering a quench liquid to remove undesired byproducts ofpyrolysis.

The method and apparatus for quenching a gas stream from the pyrolysisof EDC, when compared with previously proposed prior art methods andapparatus, has the advantages of: improving separation of the crackingfurnace effluent components of EDC, vinyl chloride, HCl, byproducts andcoke particles, which improves downstream HCl distillation efficiencyand reduces coke particle removal costs; permits cooling of the gasstream without the use of circulation pumps and associated piping,thereby eliminating pump maintenance costs and environmental hazardsassociated with pump and/or piping leaks; and increases filteringefficiency of undesired coke particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow sheet of a conventional quench column sectionin a commercial plant for the production of VCM from EDC;

FIG. 2 is a process flow sheet of another type of conventional quenchcolumn section in a commercial plant for the production of VCM from EDC;

FIG. 3 is a process flow sheet of another conventional quench columnsection in a commercial plant for the production of VCM from EDC; and

FIG. 4 is a process flow sheet of a quench column section, in accordancewith the present invention, in a commercial plant for the production ofVCM from EDC.

While the invention will be described in connection with the preferredembodiment, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a prior art quench column 50 and method forquenching a gas stream from a conventional cracking furnace (not shown)will be described. Furnace effluent gases 51, which contain vinylchloride, HCl, unreacted EDC, and byproducts, such as coke particles andchlorinated organics, pass from the cracking furnace into the lower endof quench column 50. The furnace effluent gases 51 are cooled by directcontact with cooled, liquid EDC and vinyl chloride in the quench column50. For the purpose of clarity, the term "vinyl chloride⃡ ("VCl") is usedherein when the vinyl chloride is in-process, that is, first formed andsubsequently processed in the VCl purification section of a VCM plant(not shown). The term "vinyl chloride monomer" ("VCM") is used when theVCl has been purified, that is finished, so that it meets product. VCMspecifications. The cooled, liquid EDC and VCl is obtained in thefollowing manner. Quench liquid 52 from the lower end 50b of quenchcolumn 50 is pumped by circulation pump 53 through a cooler, or heatexchanger, 54 and returned to the upper end 50a of the quench column 50through conventional piping 55 and a liquid feed distribution system 56disposed in the upper end 50a of quench column 50. The furnace effluentgases 51 are cooled by direct contact with the circulated liquid in thequench column 50. A filter 57 is disposed within piping 55 between thelower end 50b of quench column 50 and circulation pump 53, to filter outundesired byproducts of pyrolysis, such as fine coke particles (notshown). During operation of quench column 50, quench vapors includingunreacted EDC, VCl, and HCl, pass upwardly through quench column 50, andare removed from the upper end 50a of quench column 50, and are conveyedin a conventional manner to the upper end of a conventional HCldistillation column (not shown). Quench liquid, including a liquidstream of unreacted EDC, VCl, and HCl, are removed from the lower end50b of quench column 50 through conventional piping 58. The quenchliquid is conveyed in a conventional manner to the bottom of aconventional HCl distillation column (not shown). A conventional filter59 is provided in piping 58 to remove undesired solids from the quenchliquid.

As previously discussed, there are many disadvantages associated withthe quench column 50 and method of quenching illustrated in FIG. 1.Relatively large capacity circulation pumps 53 and piping 55 arerequired with the quench column 50 of FIG. 1, which increases thecapital costs associated with utilizing such a quench column 50 andmethod for quenching the furnace effluent gases. The circulated, cooledliquid which passes through piping 55 normally contains fine cokeparticles which can cause severe pump maintenance problems and erosionof piping 55. When utilizing the quench column 50 and method forquenching of FIG. 1, it is difficult to remove the fine coke particles,which in turn causes relatively high fouling rates on VCl purificationequipment (not shown). It has also been found that poor separation ofthe furnace effluent gas components is achieved, which results in higherenergy usage for the downstream HCl/VCl distillation process.Additionally, the filtering efficiency of filters 57 and 59 is typicallyvery poor because the relatively high flow velocities of circulationpump 53 tends to break up the fragile coke particles into smallerparticles which can readily pass through the filter elements of filters57, 59.

With reference to FIG. 2, another prior art quench column and method forquenching will be described. Hereinafter, identical reference numeralswill be used for identical components previously described, and primedreference numerals will be utilized for components similar to thosecomponents previously described. In the quench column 50 of FIG. 2, acirculated, cool liquid is also introduced into the upper end 50a ofquench column 50 via liquid feed distribution system 56, through the useof piping 55' and circulation pump 53, whereby the furnace effluentgases 51 are cooled by direct contact with the cooled liquid EDC and VClin the manner previously described in connection with FIG. 1. In themethod of quenching of FIG. 2, the cooled liquid EDC and VCl is obtainedby condensing quench overhead vapors of VCl, HCl, and unreacted EDCwhich pass from the upper end 50a of quench column 50 through acondenser, or heat exchanger 54, and the circulated, cooled, condensedliquid is pumped by circulation pump 53 through piping 55' and into theliquid feed distribution system 56 in the upper end 50a of quench column50. A conventional separator tank 60 is disposed within piping 55',which permits quench vapors and quench liquid to be withdrawn and fed tothe HCl distillation column as previously described in connection withFIG. 1. Solids are removed from the lower end 50b of quench column 50and pass through piping 58 and filter 59 as previously described inconnection with FIG. 1. The quench liquid from piping 58 is thenconveyed to a solids removal system (not shown) which may includetreatment of the quench bottoms liquid in a series of flash tanks (notshown) or treatment in a small stripper column (not shown) to remove HCland VCl. EDC in the quench bottoms purge stream from piping 58 isseparated from solids in an EDC tars still (not shown) or in an EDCvacuum distillation column. Removal of HCl and VCl from the quench EDCpurge stream is essential for smooth operation of these EDC distillationcolumns.

Although the quench column 50 and method of quenching of FIG. 2 offerssome improvements over the quench column 50 and method of quenching ofFIG. 1, in that the circulated liquid is relatively clean, since itcontains little or no coke particles, there are still severaldisadvantages associated with the prior art quench column 50 and methodfor quenching of FIG. 2. Large capacity circulation pumps 53 and piping55' are still required, relatively poor component separation isobtained, and there is still some degree of quench column pump and/orpiping hazards and associated maintenance costs.

With reference to FIG. 3, another prior art quench column 50 and methodfor quenching furnace effluent gases 51 will be described. Quench column50 of FIG. 3 incorporates circulation of two cooled liquid streams,which include cooled liquid EDC and VCl. The quench column 50 of FIG. 3combines the components of the FIG. 1 embodiment with the components ofthe FIG. 2 embodiment, all as previously described in connection withFIGS. 1 and 2, with the exception that cooler, or heat exchanger, 54 ofFIG. 1 is not used in connection with piping 55. Accordingly, the quenchcolumn 50 of FIG. 3 incorporates circulation of an overhead condensedliquid stream from piping 55' and a liquid bottoms stream from piping55, both of which pass into quench column 50 through liquid feeddistribution systems 56. The quench column 50 and method for quenchingfurnace effluent gases of FIG. 3 has all of the disadvantages previouslydescribed in connection with the quench columns 50 and methods forquenching, of FIGS. 1 and 2, with the further disadvantages of evenhigher capital costs for the necessary circulation pumps 53 and piping55, 55'. Additionally, because of the increased piping 55, 55' and theuse of multiple circulation pumps 53, there are even higher risks forpiping leaks and potential plant fires resulting from such leaks.

With reference to FIG. 4, the quench column 70 and method of quenching agas stream, in accordance with the present invention, will be described.Quench column 70 generally includes: a vertically disposed pressurevessel 71 having an upper end 72 and a lower end 73, the lower end 73adapted to contain a quantity of quench liquid 74; at least one nozzle75 disposed in the lower end 73 of the vessel 71, and the at least onenozzle 75 is disposed and submerged within the quantity of quench liquid74; a plurality of column fractional distillation trays 76, with atleast an upper column fractional distillation tray 77 and a bottomcolumn fractional distillation tray 78, disposed within the vessel 71,above the at least one nozzle 75 and a means for introducing 80 liquidEDC, VC1, and HCl into the upper end 72 of the vessel 71 above theplurality of column fractional distillation trays 76. Preferably, eightcolumn fractional distillation trays, of conventional design, areprovided in vessel 71.

Still with reference to FIG. 4, the means for introducing 80 liquid EDC,VCl, and HCl is preferably a knock back condenser 81 disposed in theupper end 72 of the vessel 71, and the knock back condenser 81 isdisposed above the plurality of column fractional distillation trays 76.A suitable cooling medium 82 enters the upper end 83 of knock backcondenser 81 and flows through the condenser and exits the lower end 84of knock back condenser 81 at exit pipe 85. Alternatively, as shown inphantom lines in FIG. 4, the means for introducing 80 liquid EDC, VCl,and HCl may be a horizontally disposed condenser 90, of conventionaldesign, disposed above vessel 71. A quench vapor inlet pipe 91 permitsquench vapors from vessel 71 to pass upwardly into condenser 90, andupon the quench vapors being condensed within condenser 90, liquid EDC,VCl, and HCl flow from the condenser 90 back into the upper end 72 ofvessel 71. Because condenser 90 is disposed above vessel 71, the liquidEDC, VCl, and HCl will flow from condenser 90 through pipe, or flowpassageway 92 into the upper end 72 of vessel 71 only under the force ofgravity, with no circulation pump being necessary or utilized.

Still with reference to FIG. 4, an outlet means 95, such as pipe, orflow passageway, 96 is disposed at the lower end 73 of vessel 71, andmay be utilized for draining a portion of the quench liquid 74 fromvessel 71. The outlet means 95 is in fluid communication with a meansfor filtering 97, or filter 98, of conventional design, for filteringthe quench liquid 74 to remove undesired byproducts of pyrolysis,including particles of coke. The filtered quench liquid exiting fromfiltering means 97 may then pass through conventional piping 99 and maybe conveyed directly to a solids removal system 100, or conveyeddirectly to a series of flash tanks (not shown) or a small strippercolumn (not shown) to remove HCl and VCl.

The upper end 72 of vessel 71 includes a fluid passageway, or pipe, 105for conveying quench vapors from the vessel 71 to a conventional HCldistillation column (not shown). A suitable, conventional pipe 106 is influid communication with the bottom column fractional distillation tray78, and permits the removal of a liquid stream of EDC, VCl, and HCl fromthe bottom column fractional distillation tray 78, which is conveyed toa conventional HCl distillation column (not shown).

Still with reference to FIG. 4, the method of quenching a gas streamcomprising VCl, HCl, and unreacted EDC, produced by the pyrolysis of EDCand containing undesired byproducts of pyrolysis, in accordance with thepresent invention, will be described. The hot, furnace effluent gases 51enter the lower end 73 of vessel 71 and pass through nozzle 75, which issubmerged within the quantity of quench liquid 74. The at least onenozzle 75 provides natural liquid circulation of the quench liquid 74within the lower end 73 of vessel 71, and further provides immediatecontact of the furnace effluent gases 51 with the quench liquid 74,whereby the furnace effluent gases, or gas stream comprising VCl, HCl,and unreacted EDC are immediately cooled. Accordingly, cooling of thefurnace effluent gas stream ceases the pyrolysis of the EDC andminimizes the formation of additional byproducts, while EDC, VCl, andHC1 vapors, or quench vapors, 110 rise from the quantity of quenchliquid 73 upwardly through vessel 71. As the rising quench vapors 110pass upwardly through vessel 71, the vapors 110 are partially condensedwhen they contact the coils of knock back condenser 81, whereby liquidEDC, VCl, and HCl are thereby introduced into the upper end 72 of vessel71. Liquid EDC, VCl, and HCl then flow downwardly within vessel 71,without the use of any pumps or piping, and this liquid passesdownwardly through the plurality of column fractional distillation trays76, which serve to separate the EDC, VCl, and HCl components. A liquidstream of EDC, VCl, and HCl may be removed by piping 106 from the bottomcolumn fractional distillation tray 78, which liquid stream, or quenchliquid, is then conveyed to the HCl distillation column (not shown) aspreviously described. The upwardly rising EDC, VCl, and HCl vapors, orquench vapors 110, which are not condensed by contacting knock backcondenser 81, pass upwardly through piping 105 and are conveyed to theHCl distillation column (not shown) as previously described.

Alternatively, condenser 90 may be utilized in lieu of knock backcondenser 81, as the means for introducing 80 liquid EDC, VCl, and HClinto the upper end 72 of vessel 71. Once again, the utilization ofcondenser 90 provides quench liquid 74, as well as the quench liquidswhich are drained from the bottom column fractional distillation tray78, as previously described.

It has been discovered by utilizing the plurality of column fractionaldistillation tray 76 within vessel 71, and withdrawing quench vapors 110from the upper end 72 of vessel 71 and withdrawing quench liquid fromthe bottom column fractional distillation tray 78, as previouslydescribed, four to six theoretical-separation stages may be achieved,rather than only one to two theoretical separation stages achieved witha conventional quench column of equivalent height. By increasing thenumber of theoretical separation stages within vessel 71, there is asignificant improvement in component separation. It has been found thatthe quench vapors 110 removed from the upper end 72 of vessel 71 containless EDC and more VCl and HCl, while the quench liquid removed from thebottom column fractional distillation tray 78 contains less VCl and HCl,and more EDC. Both of these results permit improved performance in theHCl distillation column, as well as improved performance of the solidremoval system 100. Table 1, set forth below, illustrates the improvedcomponent separation obtained through use of the quench column 70 andmethod for quenching a gas stream, of the present invention, whencompared with the prior art quench columns and methods of quenching ofFIGS. 1-3.

    ______________________________________                                        Quench Product                                                                              FIG. 1    FIGS. 2 & 3                                                                              FIG. 4                                     Streams       Design    Design     Design                                     ______________________________________                                        Quench Vapors Feed to                                                         HCl Column:                                                                   Weight % EDC  3.46      1.96       Trace                                      Weight % VCl  40.51     30.24      40.43                                      Weight % HCl  56.02     67.80      59.57                                      Quench Liquid Feed to                                                         HCl Column:                                                                   Weight % EDC  61.37     53.96      61.45                                      Weight % VCl  36.07     37.42      37.01                                      Weight % HCl  2.56      8.61       1.54                                       ______________________________________                                    

The foregoing data was obtained from a process computer simulation, andpreliminary lab and plant data conform to the computer simulation data.The same operating parameters for each design were utilized.

The use of the quench column 70 and method of quenching a gas stream, inaccordance with the present invention also provides increased filteringefficiency by filter 98 because of reduced quench liquid 74 flowvelocity in vessel 71 and through pipe 96 to filter 98. The cokeparticles in the furnace effluent gases 51 are quite fragile, andtypically break up into smaller particles which may pass through thefilter elements (not shown) of filter 98 when used in connection withprior art quench column designs as illustrated in FIGS. 1-3, whichoperate at higher liquid flow velocities than that of quench column 70in accordance with the present invention. Accordingly, filteringefficiency is greatly improved in the quench column 70 and method forquenching a gas stream, in accordance with the present invention. It hasbeen found that the quench liquid 74 after passing through filter 98 maybe conveyed directly to HCl and VCl distillation equipment, oralternatively, may be fed to a solid removal system 100. The improvedcomponent separation obtained by quench column 70, and the method ofquenching a gas stream, in accordance with the present invention,simplifies the design of the solid removal system 100.

Another advantage obtained through use of the quench column 70, andmethod of quenching a gas stream, in accordance with the presentinvention, is that unreacted EDC may be recycled directly back into thefeed for the cracking furnace, until the cracking furnace effluent gastemperature increases sufficiently to produce enough HCl and VCl topressure up the quench column 70, and the volume of unreacted EDC in thequench vapors is reduced enough to minimize HCl and VCl distillationboil up problems. Improved quench component separation obtained from theuse of quench column 70, in accordance with the present invention, makesthis recycle start-up technique feasible. In prior art cracking furnacestart-ups, there are typically plant operating problems due to theexcessive quantities of unreacted EDC and low quench operating pressureresulting from the use of prior art quench columns such as shown inFIGS. 1-3.

It is to be understood that the invention is not to be limited to theexact details of construction, operation, exact materials, orembodiments shown and described as obvious modifications and equivalentswill be apparent to one skilled in the art, for example, a conventionalcondenser design and pumps could be used to introduce liquid EDC, VCl,and HCl into the upper end of the quench column, above the plurality ofcolumn fractional distillation trays. Accordingly, the invention istherefore to be limited only by the scope of the appended claims.

I claim:
 1. A method of quenching a gas stream comprising vinylchloride, hydrogen chloride, and unreacted 1,2-dichloroethane producedby the pyrolysis of 1,2-dichloroethane and containing undesiredbyproducts of pyrolysis, comprising the steps of:(a) providing a quenchcolumn, having an upper and a lower end, the lower end of the quenchcolumn containing a quantity of quench liquid; (b) introducing the gasstream directly into the quench liquid to cool the gas stream to ceasethe pyrolysis of the 1,2-dichloroethane and minimize the formation ofadditional byproducts whereby 1,2-dichloroethane, vinyl chloride, andhydrogen chloride vapors rise from the quench liquid; (c) providing aplurality of column fractional distillation trays, with at least anupper column fractional distillation tray and a bottom column fractionaldistillation tray, within the quench column above the quantity of quenchliquid; (d) passing the 1,2-dichloroethane, vinyl chloride, and hydrogenchloride vapors upwardly through the plurality of column fractionaldistillation trays; (e) introducing liquid 1,2-dichloroethane, vinylchloride, and hydrogen chloride into the upper end of the quench column,above the plurality of column fractional distillation trays; (f)removing 1,2-dichloroethane, vinyl chloride, and hydrogen chloridevapors from the upper end of the quench column; and (g) removing aliquid stream of 1,2-dichloroethane, vinyl chloride, and hydrogenchloride from the bottom column fractional distillation tray.
 2. Themethod of claim 1, wherein the liquid, 1,2-dichloroethane, vinylchloride, and hydrogen chloride are introduced into the upper end of thequench column by providing a knock back condenser in the upper end ofthe quench column above the column fractional distillation tray, andpartially condensing the rising 1,2-dichloroethane, vinyl chloride, andhydrogen chloride vapors.
 3. The method of claim 1, wherein the liquid,1,2-dichloroethane, vinyl chloride, and hydrogen chloride are introducedinto the upper end of the quench column by providing a horizontallydisposed condenser above the quench column; partially condensing therising 1,2-dichloroethane, vinyl chloride, and hydrogen chloride vapors;and introducing the liquid 1,2-dichloroethane, vinyl chloride, andhydrogen chloride from the horizontally disposed condenser into theupper end of the quench column.
 4. The method of claim 3 including thestep of flowing the liquid 1,2-dichloroethane, vinyl chloride, andhydrogen chloride into the upper end of the quench column by onlyutilizing the force of gravity, whereby no pump is utilized to introducethe liquid 1,2-dichloroethane, vinyl chloride, and hydrogen chloride. 5.The method of claim 1, including the step of removing from the bottom ofthe quench column a portion of the quench liquid containing theundesired byproducts of pyrolysis.
 6. The method of claim 5, includingthe step of filtering out the undesired byproducts of pyrolysis, fromthe removed quenched liquid.